Copper based sintered contact material and double-layered sintered contact member

ABSTRACT

With the objectives of alleviating the property of attacking on the mating member by scratching-off of local agglutinates on the sliding contact surface, achieving improved wear resistance, and achieving improved seizure resistance through restraint of frictional heat generation by a hard phase, a copper based sintered contact material contains shock-resistant ceramics in an amount of 0.05 to less than 0.5 wt % as non-metallic particles composed of one or more substances selected from pulverized oxides, carbides and nitrides. The shock-resistant ceramics are comprised of SiO 2  and/or two or more substances selected from SiO 2 , Al 2 O 3 , LiO 2 , TiO 2  and MgO.

TECHNICAL FIELD

The present invention relates to a copper based sintered contactmaterial and a double-layered sintered contact member produced bysinter-bonding the copper based sintered contact material to an ironbased material.

BACKGROUND OF THE INVENTION

Generally, various copper based alloys are selected for use as a bearingmaterial according to conditions such as oil lubricating conditions,sliding speed and sliding contact surface pressure. For bearingmaterials used in oil, comparatively soft bronze (e.g., BC3 and BC6),phosphor bronze (e.g., PBC2A), lead bronze (e.g., LBC 2-5) and kelmet(e.g., KJ 1-4) casting materials are utilized. In conditions a littlepoor in oil lubricity, Cu—Sn or Cu—Sn—Pb is used as a copper basedsintered bearing material and bronzed based oil-less bearings producedby adding graphite (solid lubricant) to Cu—Sn or Cu—Sn—Pb (copper basedsintered bearing material) are often used.

In the roller sections of undercarriages for construction machines,double-layered bearings are utilized which are produced by scattering alead bronze based sintered material powder onto a metal backing,followed by sintering and rolling with a mill and by sinter bonding thesintered material to the metal backing by resintering. Suchdouble-layered bearings to which a soft metal such as Sn is overlaid arewidely used as an engine metal. Under sliding conditions with highersurface pressure, slower sliding speed and a likelihood of boundarylubrication, soft high strength brass (e.g., HBsC 1-4) having goodseizure resistance and wear resistance is utilized (see “EngineeringData Book for Copper based Alloy Casting” (pp 134-155), edited by JapanNon-ferrous Metal Casting Association, issued by Materials ProcessTechnology Center (SOKEIZAI CENTER), Jul. 30, 1988).

The recent demand for the most generally used bronze based and leadbronze based contact materials is to achieve improved seizure resistanceand wear resistance under high sliding speed conditions while ensuringexcellent wear resistance under slow sliding speed and poor lubricatingconditions. In view of the current environmental problems, it isdesirable to exert, without use of Pb, the characteristics of leadbronze sintered contact materials, namely, good comformability andconstant seizure resistance.

It is conceivable that the frequent occurrence of galling accompanied byabnormal abrasion under high speed and high surface pressure slidingconditions is attributable to occurrence of agglutination/adhesion andits rapid growth caused by a contact between the metals in boundarylubrication. In many cases, great effort is made to restrain the gallingby forming an overlaid layer from a soft metal (e.g., Sn) like the caseof engine metals, thereby achieving improved comformability and fluidlubricity. However, this technique has revealed a problem in thedurability and service life of the overlaid layer when the lead bronzebased sintered contact material is used under higher surface pressure orin a condition where boundary lubricity increases because of additionalconditions (e.g., vibration load and acceleration/deceleration) imposedon the material while the material being subjected to sliding contact.Therefore, it has become necessary to improve the sliding performanceand durability of the lead bronze based sintered contact materialitself.

On the other hand, lead bronze based and lead copper based sinteredcontact materials which contain large amounts of Pb suffer from thefollowing problem: If they are used in a condition where, among others,sliding speed is high, or where acceleration and deceleration arerepeated with changes in the rotating (sliding) direction so thatsliding speed greatly changes, or where the mating material has highsurface roughness, wear resistance will rapidly increase and as aresult, sufficient durability cannot be ensured for long use.

The aforesaid high strength brass should be utilized if importance isgiven to the improvement of the wear resistance of a contact material,but it is normally hard, having a hardness of Hv 180 or more andtherefore presents the drawbacks of poor comformability and a limitationto use under high load, low speed conditions. In addition, high strengthbrass has significantly high vapor pressure and a high concentration ofhighly oxidable Zn so that it cannot be bonded to steel by casting.Therefore, high strength brass cannot be utilized in casting-bonding tocylinder blocks, valve plates and the like which are made from ironbased material to be used for hydraulic pumps and hydraulic motors, suchcasting-bonding being one of the chief objects of the invention to bedescribed later.

Regarding wear resistance and seizure resistance, oil-impregnated copperbased sintered contact materials have more or less the same problem.Brass based sintered contact materials are also extremely difficult tobe sinter bonded to, for instance, iron based materials because of thehigh Zn concentration of the brass based material, and therefore theycannot be utilized in sinter bonding to cylinder blocks and valveplates.

In recent years, there are strong demands, in view of the environmentalproblems, towards a ban on use of Pb which is generally contained inlead bronze copper based contact materials.

A prior art bronze based sintered contact material, which has beenimproved in its characteristics from the above point of view, isdisclosed in Japanese Patent Kokai Publication Gazette No. 11-350008(1999). This publication proposes a double-layered bronze based sinteredcontact member and its bronze based sintered contact material. In thistechnique, a powder prepared by blending a bronze powder containing noPb and 3 to 13 wt % of W powder is dispersed onto a metal backing madeof a steel plate; the blended powder and the metal backing undergosintering and rolling to have high density; and then, sintering iscarried out again. According to this technique, since W has goodaffinity with respect to a bronze matrix and high bonding strength,dropping-off of W due to sliding resistance etc. does not occur. Inaddition, since W has proper hardness (W: Hv 350 to 500, Mo: Hv 200 to250), namely, being harder than a bronze matrix and softer than ceramicsparticles which are too high in hardness and likely to give damage totheir mating material, part of the W particles locally protrudes towardsthe mating contact member, forming an irregular contact surface. Thelevel difference between the convex and concave portions of theirregular contact surface forms a lubricating oil film. Further, since Whas a high melting point (3,410° C.), it does not melt unlike Pb. It isconsidered that, with these features, W keeps good sliding propertiesfree from seizure and non-uniform sliding and does not wear the matingmaterial.

The technique disclosed in the above publication has, however, aneconomical problem because the W particles to be dispersed for forming alubricating oil film need to be contained in a large amount (3 to 13 wt%). In addition, as the sliding conditions become harder with increasingcircumferential speed and increasing surface pressure, the W particlescome into local metallic contact with the mating member, formingagglutinates even though the W particles do not melt unlike Pb. The Wparticles are not hard enough and therefore a satisfactory function forscratching off the local agglutinates cannot be achieved for stoppingthe growth of the agglutinates. As a result, a satisfactory improvementin wear resistance cannot be expected and moreover, the generation of alarge amount of powder agglutinates leads to a failure in achieving asatisfactory improvement in seizure resistance.

Another technique is disclosed in Japanese Patent Kokai PublicationGazette No. 7-166278 (1995) in which 0.5 to 5 wt % Mo or 0.5 to 15 wt %Fe—Mo is added to a bronze based sintered contact material and/or a leadbronze based sintered contact material, whereby excellent lubrication aswell as good affinity with respect to oil are imparted to attain a lowfriction coefficient and high wear resistance. This technique has provedunsuccessful in that, like Japanese Patent Kokai Publication No.11-350008, the hardness of the Mo particles is not hard enough,entailing an unsatisfactory improvement in wear resistance and thegeneration of a large amount of agglutinated powder leads to anunsatisfactory improvement in seizure resistance.

In the producing method described in Japanese Patent Kokai PublicationNo. 7-166278, bronze based and/or lead bronze based sintered contactmaterials are compacted to form a green compact which is in turn fit toan iron metal backing plated with copper, and thereafter, a pressure of10 kg/cm² or less is applied to carry out pressure sintering and sinterbonding, thereby providing a double layered sintered member havingimproved mechanical strength in the sintered compact. This producingmethod involves pressure sinter bonding and therefore imposes manygeometric restrictions on its applications as well restrictions onequipment to be employed, which results in not only poor productivitybut also high production cost. Additionally, in cases where Pb which isthe most effective material for ensuring good comformability is added ina large amount, Pb is likely to flow out of a sintered compact whensintered in a pressurized condition because Pb is a metal element havinga low melting point. A large amount of Sn or the like also flows outtogether with Pb so that not only large amounts of Sn and Pb cannot becontained in the above sintered contact material but also the flow-outof Sn and Pb through the production process causes an environmentalproblem.

Another well-known method is such that with a view to improvingcomformability and seizure resistance under severe lubricatingconditions with high surface pressure and low sliding speed, a layeredsolid lubricant such as molybdenum disulfide (MoS₂), tungsten disulfide(WS₂) or graphite is added to a copper based sintered contact material.This technique has however revealed the problem that since molybdenumdisulfide and tungsten disulfide tend to be decomposed into hard coppersulfide (Cu₂S) during sintering, it becomes necessary to add thesedisulfides in large amounts in order to ensure sufficient lubrication.This results in brittleness in the sintered compact and an increase inthe cost.

Graphite does not react to a bronze based or lead bronze based sinteredmaterial, markedly restrains the sinterability of the sintered compact,weakens the strength of the sintered material, and is hardly wet by Snrich and Pb rich liquid phases which are generated during sintering.Therefore, addition of graphite presents the problem that sweatingbecomes significant during sintering, producing a number of melt-offpores. In addition, boundary lubrication is promoted by the facts thatas the amount of residual graphite increases, it becomes more difficultto compact the sintered layer and that graphite is a porous substance.In consequence, sliding properties under high-speed oil lubricatedconditions cannot be improved as much as expected.

In the field of porous bronze based sintered materials which are used asa friction material for brakes and clutches in applications havingutterly different purposes from those of contact materials for bearings,there have been developed materials capable to exhibit a high frictioncoefficient property for stopping a high speed rotor in a dry, semi-dryor boundary lubricating condition. These materials contain, as shown inTables 1 to 3 (quoted from the report written by Hanazawa in “Journal ofthe Japan Society for Composite Materials” 3(1), 8, 1977; “Industriesand Products” No. 59; and “Ceramics Data Book 76” p. 336, 1976), largeamounts (5 to 15 wt %) of graphite as a base thereby to ensure porosityand low Young's modulus, and further contain heat-resistant metals(e.g., graphite and Mo) which are solid lubricants having excellent heatresistance to prevent the fusion and seizure of the mating material atthe time of braking. Further, they contain 3 to 20 wt % hard particles(non-metallic particles) such as SiO₂ and mullite thereby restrictingthe plastic flow of the friction material metal base and properlyscraping off the surface of the mating material to achieve animprovement in the wear resistance of the friction material and a stablehigh friction coefficient.

TABLE 1 The compositions of typical metalic cermet friction materials(wt %) ingredients lubricating metalic ingredients wear-resistantingredients ingredients categories Cu Sn Zn silica mulite iron Mographite Pb metalic-1 67.3 5.3 4.4 7.1 7.1 8.8 metalic-2 60˜75 5˜10 2˜75˜7 5˜10 5˜10 metalic-3 62 7 4 8 7 12 cermet-1 60 5 20 5 10 cermet-2 505 20 10 5 10 cermet-3 47 3 5 4 20 8 5 8

TABLE 2 The typical compositions of cermet brake linings for aircraft(wt %) ingredients lubricating metalic ingredients wear-resistantingredients ingredients categories Cu Sn Zn silica mulite iron Mographite Pb example 1 Bal. 3˜10 3˜10 20˜30 5˜10 example 2 60 5 20 5 10example 3 50 5 20 10 5 10

TABLE 3 The typical compositions of cermet friction materials forgeneral purpose (wt %) ingredients metalic lubricating ingredientswear-resistant ingredients ingredients categories Cu Sn Zn silica muliteiron Mo graphite Pb Bi example 4 Bal. 5˜10 3˜6 3˜6  5˜10  5˜10 example 5Bal. 3˜6  3˜6 4˜6 example 6 Bal. 5˜10 3˜5 3˜5 10˜15 10˜15 example 7 Bal.3˜6  3˜6 3˜5  5˜10 5˜10

If these friction materials are used as a sliding material such asdisclosed in the present invention, there arise the following problems.

(1) The exothermic reaction caused at the contact surface by a highfriction coefficient becomes a problem.

(2) Since the non-metallic powders are high in hardness, they causeexcessive wear of their mating material.

(3) Since a large amount of the non-metallic material is unlikely to bebonded to the metal base, the strength of the sintered compact decreasesand the wear resistance of the friction material itself is insufficient.Further, the non-metallic material is likely to drop off the frictionsurface so that the dropped powder sometimes galls other parts than thefriction area.

(4) The friction materials and their mating materials are designed onassumption that they are periodically replaced as consumables.

The suitability of hard dispersion particles as a bronze based sinteredfriction material is described for example in Published JapaneseTranslations of PCT international Publication for Patent ApplicationsNo. 7-508799 (1995). In this publication, it is disclosed that amaterial having a friction coefficient as high as possible andindependent of temperature, sliding speed, contact pressure and otherscan be obtained by adding hard particles in an amount of 5 to 40 wt %,the particles having a size of 50 to 300 μm and hardness of HV 600 ormore and containing, for instance, carbides of Cr, Mo, W and/or V,nitrides of Al and/or Mo, and/or oxides of Cr, Ni and/or Zr. However, itis apparent that the friction coefficient of this material is so highthat it cannot be utilized as a bronze base contact material and thismaterial also suffers from the same problem as described earlier.

Regarding double layered sintered contact members such as engine metalsformed by sinter bonding the above lead bronze based sintered contactmaterial to a steel plate, since their production method involves sinterbonding carried out in a condition where an alloy powder having acomposition of a lead bronze based sintered contact material isdispersed on a steel plate, the dispersed alloy powder is shrunk duringsintering when sinter bonding is performed at a temperature which is atleast equal to or higher than the peritectic temperature (about 800° C.)of Cu—Sn, so that the alloy powder is likely to come off during sinterbonding. When sinter bonding a bronze based alloy powder containing noPb, the sintering temperature needs to exceed the peritectic temperaturein order to produce a liquid phase essential for sinter bonding. Thedispersed alloy powder shrinks more significantly than the lead bronzebased material during sintering and therefore the alloy powder cannot besinter bonded to the steel plate.

The present invention is directed to overcoming the above-describedshortcomings. Therefore, a primary object of the invention is to improvethe seizure resistance and wear resistance of a copper based sinteredcontact material while alleviating attacks on its mating materialthrough scratching-off of local agglutinates on the sliding contactsurface, by adding a proper amount of a hard dispersion phase havinggood agglutination resistance with respect to iron to the copper basedsintered contact material, or to provide an inexpensive copper basedsintered contact material having an improved critical seizure point byfurther adding a soft dispersion phase having good agglutinationresistance and good lubricity to the copper based sintered contactmaterial to restrain frictional heating caused by the hard phase.

A secondary object of the invention is to provide an inexpensivedouble-layered sintered contact member which is produced by dispersing apowder of a bronze based or lead bronze based sintered material onto asteel plate and then sinter bonding the dispersed powder to the steelplate, and to which stable sinter-bondability is imparted by addingelements for restraining the sinter shrinkage of the dispersion layerand/or elements for expanding the dispersion layer.

DISCLOSURE OF THE INVENTION

The above objects can be accomplished by a copper based sintered contactmaterial which exerts good sliding contact properties not only in a highspeed, high surface pressure condition but also in a low speed, highsurface pressure condition. In view of this, the inventors havedeveloped a copper based sintered contact material having the followingfeatures:

(1) By properly selecting non-metallic hard dispersion particles such asceramics and intermetallic compound particles (hard, first dispersionparticles) which have good agglutination resistance with respect to iron(mating material) and good thermal shock resistance and properlydetermining the amount of the above materials and the size of thedispersed phase, an action for scratching off agglutinates locallyexisting on the sliding contact surface is caused so that improvedseizure resistance and wear resistance are obtained while reducingattacks on the mating material.

(2) To cope with severer sliding conditions, a soft dispersion phase(second dispersion particles) having good agglutination resistance andgood lubricity is added to a copper based sintered contact material,whereby frictional heating caused by the hard phase is restrained andthe critical seizure point (sliding property) is improved.

According to the invention, non-metallic hard dispersion particles(e.g., ceramics) and intermetallic compound particles which have goodagglutination resistance with respect to iron and good thermal shockresistance are finely dispersed in a copper based sintered contactmaterial to reduce attacks on its mating material as much as possible sothat improved seizure resistance is achieved while the amount of Pb tobe added is reduced or Pb is disused.

In addition, metal particles and/or alloy particles such as Mo, W, Cr.Fe and Co which cause remarkable phase separation relative to Cu aredispersed to reduce the crystal particle diameter of the copper basedsintered contact material, and Pb and intermetallic compounds are finelydispersed to achieve improved seizure resistance. Further, the hard,first dispersion particles are dispersed to achieve improved wearresistance and seizure resistance. Among others, bronze based and leadbronze based sintered contact materials, in which the hard, firstdispersion particles (i.e., the non-metallic particles and intermetalliccompound particles) are dispersed in small amounts and particles of Mo,W and the like are dispersed, have proved to be excellent in seizureresistance and wear resistance when sinter bonded to the bottom surfaceof a cylinder block for hydraulic pumps and motors, the cylinder blocksliding in a centrifugal whirling (described later) manner in a highspeed, high surface pressure condition. It has been found that Fe—Calloy particles having a carbon content of 0.15 wt % or more produce ahard martensitic structure when they are cooled after sintering orsubjected to other heating treatments so that improved wear resistancecan be easily attained.

In the present invention, emphasis is placed on achievement of thesinterability of a copper based sintered contact material like the caseof the cylinder block and on use of a copper based sintered contactmaterial sinter-bonded to an iron based material. It has turned out thatthe bondability of a copper based sintered contact material relative toan iron based material can be significantly increased by adding 1 to 16wt % Sn thereby to make a liquid phase having good wettability withrespect to an iron based material appear and by adding alloy elementssuch as Si, Al, Ti, Cr and P.

It has also been found that where Sn is added in an amount of more than12 wt %, the liquid phase normally existing in sintering at atemperature of 800° C. or more is changed to a Cu—Sn intermetalliccompound (δ phase) precipitating in the grain boundary in the course ofcooling and solidification and a β phase also finely precipitates in thematrix so that extendibility is restrained and agglutination issignificantly alleviated. This is particularly important for thecondition in which a sliding contact occurs in a centrifugal whirlingmanner (described later) like the case of cylinder blocks for hydraulicpumps and motors. This is also useful for contact materials in which theaforesaid intermetallic compound phase is dispersedly precipitated inlarge amounts and for contact materials to which hard particles such asoxides, carbides and nitrides are added in small amounts.

In the case of a double-layered sintered contact member in which a mixedpowder of a bronze based sintered material powder and a lead bronzebased sintered material powder is applied to a steel plate for sinterbonding, the dispersing alloy powder is more significantly shrunk thanlead bronze based materials, causing a sinter bonding defect relative tothe metal backing. It has been found that stable sinter bondability canbe ensured by adding an element which restrains the sinter shrinkage ofthe dispersion layer in order to prevent such a defect.

Specifically, according to a first aspect of the invention, there isprovided a copper based sintered contact material in which non-metallicparticles, comprised of one or more substances selected from the groupconsisting of pulverized oxides, carbides, nitrides and carbonitrides,are dispersed in an amount ranging from 0.2% by volume or more to lessthan 4% by volume.

Preferably, the non-metallic particles are thermal-shock-resistant,oxide-based ceramics comprising SiO₂ and/or one or two or more elementsselected from the group consisting of Si, Al, Li, Ti, Mg and Zr (asecond aspect of the invention). The non-metallic particles may have anaverage particle diameter of 70 μm or less and more preferably are inthe form of granules and/or fibers having a size of 45 μm or less (afourth aspect of the invention).

According to the invention, where carbides, nitrides and carbonitridesare utilized as the non-metallic particles, WC, TiC, TiN, TiCN, MO₂C,Si₃N₄ and the like, which are often contained in materials for cuttingtools, are preferably used as the non-metallic particles and the averageparticle diameter of them is adjusted to 5 μm or less. If thesegregation of the particles becomes a problem when blending them, it ispreferable to use cemented carbide particles mainly containing Co—Wchaving an average particle diameter of 70 μm or less, cermet particlesmainly containing Ni—TiCN, and a high speed tool steel powder in whichcarbide such as MO₂C and WC precipitates (a third aspect of theinvention).

According to a fifth aspect of the invention, there is provided a copperbased sintered contact material in which one or more kinds ofintermetallic compounds each comprising two or more elements selectedfrom the group consisting of Ni, Si, Ti, Co, Al, V and P are dispersedand the total amount of the two or more elements selected from Ni, Si,Ti, Co, Al, V and P is within the range of from 0.5 to 10 wt %.

According to a sixth aspect of the invention, there is provided a copperbased sintered contact material in which one or more kinds ofintermetallic compounds each comprising two or more elements selectedfrom the group consisting of Cu, Sn, Ca, Mn, Cr, Mo, W, Sb and Te aredispersed and the amount of the one or more intermetallic compounds iswithin the range of from 0.1 to 10% by volume.

Preferably, the intermetallic compounds of the fifth aspect and the sixaspect coexist (a seventh aspect of the invention). Preferably,non-metallic particles comprising one or more substances selected fromthe group consisting of the oxides, carbides, nitrides, carbonitridesand borides are contained in an amount which ranges from 0.1% by volumeor more to less than 4% by volume and the total amount of the dispersionphase of the non-metallic particles is 0.1 to 10% by volume (an eighthaspect of the invention).

According to each of the above aspects, metal and/or alloy particlescomprising Mo, W, Cr, Co, Fe and Fe—C are preferably dispersed in anamount of 0.5 to 5.0 wt % (a ninth aspect of the invention). Further, itis preferable that 1 wt % or less MnS and/or 1 wt % or less graphite becontained (a tenth aspect of the invention). In this case, the averageparticle diameter of MnS and/or graphite may be 20 to no more than 200μm (an eleventh aspect of the invention).

Preferably, in each of the above aspects, at least 1 to 16 wt % Sn iscontained and 0 to 25 wt % Pb is contained (a twelfth aspect of theinvention). It is also preferable that 12 to 16 wt % Sn be added and aCu—Sn compound phase be dispersedly precipitated in the structure of thesintered contact material (a thirteenth aspect of the invention). Inthis case, it is preferable that one or more alloy elements selectedfrom the group consisting of Zn, Mn, Be, Mg, Ag and Bi and a solidlubricant such as MoS₂, CaF₂ and WS₂ be contained (a fourteenth aspectof the invention).

(1) Selection of Ingredients for the Hard, First Dispersion Particles

It is disclosed in Published Japanese Translations of PCT internationalPublication for Patent Applications No. 7-508799 that a certain materialhaving the highest possible friction coefficient and independent oftemperature, sliding speed and contact pressure can be obtained byadding 5 to 40 wt % suitable hard dispersion particles selected from,for instance, the carbides of Cr, Mo, W and V; the nitrides of Al andMo; and the oxides of Cr, Ni and Zr, such particles having a size of 50to 300 μm and hardness of HV 600 or more. If the selection range for thehard particles includes SiO₂, Al₂O₃ and mullite, it can be amplified asa wide range of compound phases. On the other hand, the invention aimsto provide a contact material having the lowest possible frictioncoefficient over a wide range of sliding speeds and contact pressuresand exhibiting excellent wear resistance and seizure resistance for thepurpose of restricting attacks on its mating material (iron basedmaterial) as much as possible. From this point of view, the inventorshave developed a copper based contact material in which wear resistanceis attained by the pulling-off action of the hard, first dispersionparticles whereas excellent comformability, seizure resistance and wearresistance are assured in both low speed and high speed conditions byselecting suitable ingredients and properly determining their amountsand sizes.

(1-1) Oxides, Carbides, Nitrides and Carbonitrides (Hard Non-metallicParticles)

As described earlier, it is generally conceivable that the pulling-offaction of the hard, first dispersion particles (non-metallic particles)becomes more significant with more improved wear resistance, as thehardness and size of the non-metallic particles increase. However,seizure resistance and wear resistance cannot be simply improved byincreasing the hardness of the first non-metallic particles. Forexample, when hard particles of ZrB₂, Al₂O₃ and SiO₂ were respectivelyadded in an amount of 0.3 wt % (this experiment will be describedlater), it was found that ZrB₂ (Hv=3000) exhibited the worst seizureresistance, with Al₂O₃ (HV=2000), SiO₂ (Hv=780) in that order.

It has also been found from the comparison data on Al₂O₃ and SiO₂ havingdifferent sizes that as the size of Al₂O₃ increases, wear resistanceremarkably increases while seizure resistance decreasing and that thesize of SiO₂ does not considerably affect these properties.Particularly, in the case of Al₂O₃ hard particles having higher hardnessthan its mating material (the surface hardness of a carburized quenchedsteel=Hv 900), as the particle diameter of Al₂O₃ increases, attacks onthe mating material becomes more significant. In the case of hardnon-metallic particles (e.g., Al₂O₃ and TiN) having Hv 1,000 or more, itis desirable to disperse fine particles having an average particlediameter of 5 μm, because attacks on the mating material can bealleviated.

Regarding hard particle size, significant attacks such as caused byAl₂O₃ were not observed in the case of SiO₂ and ZrO₂ having an averageparticle diameter of about 20 μm. Provably, this result is attributableto the facts that these particle materials are not as hard as Al₂O₃ and,particularly, SiO₂ makes a gentle pulling-off action because its Youngmodulus is lower than those of Cu alloys (serving as a base material)and steel (serving as a mating material) and that SiO₂ has high strengthrelative to a thermal shock stress which is likely to occur while SiO₂making a pulling-off action on the sliding contact surface as describedlater.

In the constant rate friction abrasion test which was conducted on anAl₂O₃ ceramics sintered compact under a lubricating condition prior tothe tests conducted on Examples of the invention (described later), theAl₂O₃ ceramics sintered compacts presented an extremely low seizurelimit value (PV value) in a high speed sliding condition. The reason forthis is that destructive wear particles were produced by a thermal shockstress imposed on the Al₂O₃ sliding contact surface. This is apparentfrom the report written by Tsukamoto, Takahashi, Komai, Hayama et. al.in “Powder and Powder Metallurgy” 31, p290 (1984) in which they reportedthat Al₂O₃ in a friction material was destroyed by a thermal shockstress.

With the above facts, the inventors have clarified that since the hard,first non-metallic particle material needs to be involved in thepulling-off action at the sliding contact surface as described earlier,it must meet the following requirements as a hard dispersion particlematerial for the copper based sintered contact material: (1) theparticle material must posses an adequate hardness of Hv 350 or more;(2) the particle material must provide excellent agglutinationresistance relative to iron (mating material); and (3) the particlematerial must have excellent thermal shock resistance, when takingaccount of the fact that the non-metallic particles are subjected to asevere thermal shock caused by rapid heating and rapid cooling when thepulling-off action takes place on the sliding contact surface.

To attain excellent thermal shock resistance, the non-metallic particlesshould have at least one of the following properties which are: (1)extremely low thermal expansion coefficient; (2) high heat conductivity;(3) low Young modulus; and (4) plastic deformability.

SiO₂ proposed by the invention has a considerably small thermalexpansion coefficient and low Yong's modulus equal to or lower than thatof copper as described earlier. Further, it has nearly the same hardnessas that of quenched steel as described earlier and makes less attacks onthe steel material. Taking these characteristics into account, it isapparent that SiO₂ is the optimum material. As a thermal-shock-resistantmaterial similar to SiO₂, cordierite, spodumen, eucryptite, Al₂O₃, TiO₂or the like is apparently suitably used.

It is also obvious that even if the material of the non-metallicparticles is brittle under a thermal shock stress like Al₂O₃ mentionedabove, brittleness can be overcome by fining the particles to bedispersed so as to have a grain size of 5 μm or less.

Hard dispersion particles of carbides, nitrides and carbonitridesgenerally have excellent heat conductivity and therefore excellentthermal shock resistance. Further, the carbides, nitrides andcarbonitrides of WC, TiC, TiCN, Si₃N₄, TaC, HfC, ZrC, Mo₂C, VC areuseful, as apparent from the following example of TiN addition(described later) and from the fact that they are used in the productionof cutting tools made from iron based materials. Since the harddispersion particles of these materials are extremely fine, having anaverage particle diameter of 2 μm or less because of their producingmethod, there sometimes arises a problem in their uniform dispersibilitywhen dispersed in a copper based sintered contact material. Therefore,the invention utilizes, as the hard, non-metallic particles, cermetparticles comprised of these carbides, nitrides, carbonitrides, Co andNi, because such cermet particles are excellent in terms of thermalshock resistance. The average size of the cermet particles to be addedis not particularly specified but preferably adjusted to 70 μm or lessif required in the post treatment.

As described earlier, where the non-metallic particles are too hard(e.g., Hv=1,000 or more), the dispersion particles are fined to 5 μm orless in order to alleviate the mating material-attack property. In thecase of SiO₂ (HV=780) and ZrO₂ (Hv=1,050) having an average particlesize of 20 μm, a significant attack property as is in Al₂O₃ was notobserved and it is therefore conceivable that no serious problem iscaused even when a proper average grain size for the dispersionparticles having a hardness of Hv 1,000 or less is determined to beabout 70 μm (equal to the grain size of powder for general metallurgicaluse). However, taking account of the fact that the attack propertybecomes more insignificant as the dispersion particles become finer, thegrain size of the dispersion particles is preferably 45 μm or less forensuring more safety and more preferably 10 μm or less in view of theirdispersibility into the crystal grains of the sintered material(described later).

Since addition of non-metallic particles generally spoils thesinterability of a copper based sintered contact material and pulverizednon-metallic particles having a size of 1 μm or less causes significantaggregation between particles, it is difficult to uniformly mixnon-metallic particles with powder for general metallurgical use.Therefore, there is a risk that the non-metallic particles disperse in alinked fashion within the grain boundary of the resulting sinteredcompact; the sintered compact has aggregation and brittleness; andbondability cannot be ensured when the mixed powder for sintered contactmaterial is sinter bonded to the metal backing after dispersion of itonto the metal backing as described later. It is obvious from the abovefact that SiO₂, ZrO₂ SiO₂, cordierite, spodumen, eucryptite, Al₂O₃ TiO₂and the above-described cermet particles, which do not require fining,are most suitably used as the non-metallic particles. Addition offiber-like or needle-like non-metallic particles in place of a finenon-metallic powder is desirable in view of prevention ofsegregation/separation at the time of the blending and dispersiondescribed above. Al₂O₃ TiO₂, which has particularly good availability,may be used in the form of fibers.

The amount of the non-metallic particles to be added to the contactmaterial may be 4% by volume and more preferably 2% by volume, for thefollowing reasons. The maximum effect of improving wear resistance isachieved with 1.0 wt % SiO₂ and Al₂O₃ particles and where the densitiesof SiO₂ and Al₂O₃ are 2.2 g/cm³ and 3.9 g/cm³ respectively, the areapercentages (volume percentages) of SiO₂ and Al₂O₃ at the slidingcontact surface are about 4.0% and 2.2% respectively. Therefore, theeffect of the dispersion of the hard particles upon the improvement ofthe wear resistance of the contact material becomes adequate when thearea percentage (volume percentage) of the non-metallic particles issubstantially 4% by area. If the non-metallic particles are added more,a friction coefficient meaninglessly increases with the mating materialattack property becoming more significant. The proper lower limit forthe amount of the non-metallic particles is 0.2% by volume with whichthe wear resistance improving effect starts to emerge more distinctly.

When a test was made for investigating the relationship between thehardness of the matrix (Hv=40 to 160) and the proper amount of thenon-metallic particles in various contact materials, it was found thatas the hardness of the matrix increases, the above effect could beachieved with a less amount of e.g., Al₂O₃ and that the amount of Al₂O₃in this case ranged from 0.05 to 0.5 wt %. For example, in the case ofCu—25 wt % Pb (lead copper sintered contact material) which is anextremely soft material, the amount of SiO₂ to be added is conceivablyup to about 2.0 wt %. The area percentage of SiO₂ at the sliding contactsurface is about 8% by area. The conceivable reason for the increase ofthe proper amount of the hard particles is that the power of the hardparticles for scratching off the agglutinates of the mating materialdecreases in proportion to the hardness of the matrix. When takingaccount of the wear resistance improving effect of the soft matrixcontact material Cu—25 wt % Pb in conjunction with the mating materialattack property, the proper amount of the hard non-metallic particles iswithin the range of from 0.05 to 1.0 wt %. On the other hand, whengiving importance to the mating material attack property, it isdesirable to restrict the amount of the non-metallic particles to 0.5 wt% or less. In addition, in the case of bronze based and/or lead bronzebased sintered contact materials containing Pb in an amount of less than10 wt %, the amount of the non-metallic particles is preferably 0.5 wt %or less.

For the structure of the contact material after sintering, it isundesirable to let the non-metallic particles string out in the grainboundary but desirable to disperse most of the non-metallic particlesinto the crystal grains of the copper based sintered contact material.In the invention, the amount of the non-metallic hard particles requiredfor the invention is very small, say, less than 4% by volume and morepreferably about 2% by volume (0.5 wt % in the case of SiO₂). Where thenon-metallic particles have an average particle diameter of 10 μm orless and sintering is carried out on condition that the resulting copperbased sintered contact material is sufficiently compacted, most of thenon-metallic particles are entrapped in the grains because of the growthof the grains during sintering, so that brittleness is furthermitigated.

In order not to impair the comformability of the sintered contactmaterial, it is preferable that the hardness of a sintered contactmaterial containing the non-metallic particles is the substantially thesame as that of a sintered contact material containing no non-metallicparticles (the changes in hardness caused by addition of thenon-metallic particles is 10% or less). In the invention, the increasein hardness caused by addition of 0.05 to 0.5 wt % the non-metallic hardparticles is substantially negligible so that the comformability of thesintered contact material is not spoiled.

As described later, it has been found from an investigation conducted onMo and W that dispersion of Mo, W has little effect of improving,particularly, wear resistance and that the non-metallic hard particlesare the most suitable material for the hard particles dispersed in smallamounts for improving the wear resistance of the copper based sinteredcontact material. In addition, it has been confirmed that remarkablewear resistance improving effect and seizure resistance improving effectcan be achieved by addition of less than 2% by volume of the hardparticles in combination with Mo and W.

(1-2) Intermetallic Compounds

Generally, intermetallic compounds are known to be much harder thanmetals but have properties (e.g., good thermal shock resistance andplastic deformability) more similar to metals than the aforesaid oxides,carbides, nitrides and carbonitrides. Tsukamoto, Takahashi, Komai,Hayama et. al. investigated cases where large amounts of variousintermetallic compounds were added, with a view to attaining highfriction coefficients and an improvement in the wear resistance offriction materials and reported in “Powder and Powder Metallurgy” 31, p.290 (1984) that intermetallic compounds suited for friction materialshad a hardness of Hv 350 or more and a softening temperature of 400° C.or more. However, as obvious from the cases of ZrB₂ and Al₂O₃ describedabove, the sliding properties cannot be simply improved by optimizingthe hardness of the intermetallic compounds.

In the invention, with a view to achieving good sliding propertiesand/or wear resistance not only by optimizing the hardness of theintermetallic compounds but also by allowing the intermetallic compoundsthemselves to exhibit good seizure resistance, the intermetalliccompounds, which comprise elements unlikely to develop localagglutination voluntarily even if the intermetallic compounds locallyagglutinate to their mating iron based materials, are clarified based ona thermodynamic method. For obtaining such intermetallic compounds,elements which satisfy the following conditions are selected: (1) Thethermodynamically excessive energy when Fe and the elements constitutingthe intermetallic compound are alloyed by agglutination at their contactfaces has a great positive value; and (ii) Fe and the elementsconstituting the intermetallic compound chemically repel each otherwithin the agglutinative alloy.

(1-2-1) Intermetallic Compounds Comprising Two or More Elements whichStrongly Thermodynamically Repel Fe.

If the thermodynamically excessive energy when Fe and the elementsconstituting the intermetallic compound are alloyed by localagglutination at the sliding contact surfaces has a great positive valueand the energy state after the alloying is more unstable than the statebefore the alloying (endothermic reaction), local agglutination does notprogress by itself and the intermetallic compounds, that satisfy theabove conditions, are apparently excellent in seizure resistance. Suchintermetallic compounds that satisfy the above conditions need tocomprise elements which strongly repel Fe.

An element “M” which strongly repels Fe is analyzed such that athermodynamic interaction parameter Ω FeM associated with Fe and theelement “M” contained in an Fe-M alloy has a great positive value. Inthe Fe-M binary phase diagram, the element “M” is represented by thephase separation in which Fe and “M” do not homogeneously mix with eachother. More extremely, it is represented by a phase diagram in which “M”is not dissolved in a solid state within Fe because of the repellingforce of their atoms. More concretely, the element “M” is specified asfollows according to the Hansen phase diagram. (1) Examples of theelement “M”, which has proved to cause phase separation relative to Feand thermodynamically satisfy Ω FeM>>0, include Be, Cr, Mo, W, Mn, Cu,Au, Zn, Sn, Sb, S and O. (2) Examples of the element, which hardlydissolves in a solid state, include Pb, Bi, Ag, Li, Na, K, Mg, Ca, Rb,Sr, Ba, Cd and Te.

Accordingly, in view of not only the sliding properties but alsostrength, it is preferable to produce a copper-alloy based sinteredcontact material by adding one or more Fe-repelling alloy elements to acontact material containing Cu as a chief component, Cu forming adistinct phase separation line in the Cu—Fe phase diagram. In view ofthe cost performance of a sintered contact material, it is preferable todispersedly precipitate Cu—Sn based intermetallic compounds such as δ, βand γ phases in a bronze based sintered material to which a large amountof Sn has been added in order to increase the strength and sinterabilityof Cu. From the same viewpoint, dispersion of CaCu₃, Ca₂Sn, CrMn₃,Ca₃Sb₂, Ca₃Tl₄ and the like is effective. Further addition of alloyelements such as Zn, Be, Cr and Mn with the intention of achieving highstrength is desirable for a contact material.

Since Mo and W are elements which not only repel Fe but also stronglyrepel Cu and Sn which are the chief components of a bronze basedmaterial, they are dispersed as metal particles within a bronze basedsintered contact material, functioning to improve the seizure resistanceof the bronze based sintered contact material. However, Mo and W are notas hard as the aforesaid ceramics and intermetallic compounds (Mo═Hv180; W═Hv 120 to 350; Cr═Hv 700 to 800), they do not provide improvedwear resistance.

Cr also strongly repels Cu and Sn and is therefore dispersed in a bronzebased sintered contact material as metal particles. In addition, Cr isharder than Mo and W. Therefore, it is expected that the scratching-offaction of Cu is marvelous and highly improved wear resistance can beachieved by addition of a small amount of Cr. However, the repellingpower of Cr is not as strong as Mo and W and accordingly, the seizureresistance improving effect of Cr is small.

With a view to ensure both wear resistance and seizure resistance, themain feature of the invention resides in utilization of the aforesaidhard particles and intermetallic compounds in combination with Cr, Moand W particles. Since Cr, Mo and W particles do not have a significantmating material attack property, the proper amount of Cr, Mo and Wparticles is greater than the amount of the ceramics and intermetalliccompounds, being less than 5 wt %. More preferably, the amount of Cr, Moand W particles falls within the range of from 0.5 to 2.0 wt % on theground that the effect of addition of these particles becomessatisfactory when the amount of these particles is 0.5 wt % and reachesits peak when their amount is around 2 wt % and that addition of a largeamount of these particles leads to increased cost. One of the featuresof the invention is such that if Cr, Mo and W are added in a largeamount, the crystal grains of a lead bronze based sintered contactmaterial are significantly pulverized, while Pb and the Cu—Snintermetallic compound being finely dispersed, so that markedly improvedhigh-speed sliding properties can be achieved.

The action of pulverizing the crystal grains can be achieved by addingCo and Fe which are element strongly repelling the chief component of abronze based material, Cu, and/or by dispersing an FeCo ordered phase orFe—C alloy. The pulverization of the crystal grains is expected toprovide an improvement in the high-speed sliding properties of bronzebased and lead bronze based sintered contact materials.

For increasing the seizure resistance of Fe—C alloys with respect totheir mating iron based material, it is preferable to utilize amartensitic structure which is quench-hardened through a cooling processsubsequent to sintering or another thermal treatment.

(1-2-2) Emergence of Phase Separation Caused by a Combination of Two orMore Metal Elements Satisfying Ω FeM<<0 and Intermetallic Compounds

In the foregoing description, as the intermetallic compounds serving asa hard non-metallic dispersion phase, examples of the intermetalliccompounds which comprise two or more elements repelling Fe have beenexplained. It has been also thermodynamically testified that, in theternary Fe phase diagram, phase separation occurs in a combination oftwo or more metal elements which strongly attract Fe (Ω FeM<<0) andattract each other. Accordingly, the same effect of improvingagglutination resistance and wear resistance as described earlier can beobtained by dispersing one or more intermetallic compounds containingtwo or more such elements in combination.

More concretely, most of the elements which attract Fe generally form anordered phase according to their phase diagrams. Although there are someelements which do not form an ordered phase according to their phasediagrams, most of them have proved by measurements to satisfy Ω FeM<<0.Examples of such elements include Al, Si, P, Sb, Ti, V, Co, Ni, Fe, Zr,Nb, Pd, Hf, Ta and Pt. In cases where one or more intermetalliccompounds comprising two or more elements which attract each other andare selected from the above group are dispersed in a copper basedcontact material, good agglutination resistance can be ensured similarlyto the foregoing cases represented by Ω FeM>>0.

In the following embodiments, the relationship between the dispersionprecipitation amount and sliding properties of an Ni—Si intermetalliccompound (Ni₃Si) is clarified taking a high-strength Cu—Ni—Sn basedsintered contact material for example. In this case, it has beenconfirmed that the precipitation of a fine intermetallic compound leadsto improved agglutination resistance; the co-existence of the ceramicsbased dispersion particles, MnS and graphite leads to considerablyimproved wear resistance and agglutination resistance; the same effectas is in a dispersion of the phase separation type metal particles isobserved; and a dispersion of NiAl₃ and Ti₂P entails improvedagglutination resistance and wear resistance. Intermetallic compoundssimilar to the above intermetallic compound are each comprised of two ormore elements selected from the group consisting of Ti, V, Fe, Ni, Co,Al, Si and P. Among them, Si based intermetallic compounds are hard,having a hardness of more than Hv 1,000 in many cases and therefore itis preferable to disperse Si based intermetallic compounds having aparticle diameter of 5 μm or less.

Although FeCo, Fe₃Al, FeAl, FeSi, Fe₃Si are ordered phases of the BCCstructure, they are all treated as intermetallic compounds.

Further, most of the aforesaid Al compounds, Ti compounds and/or Pcompounds (phosphide) do not have a Vickers hardness exceeding Hv 900.Therefore, their attack properties are not a problem in cases where acarburized and quenched steel is used as their mating material. If themating material is worn out resulting from precipitation of hard Ti₂P(described later), the amount of Ti₂P should be reduced of course, butit is also desirable to add, in combination, the above-describedlubricating substances such as MnS and graphite.

Representative examples of the intermetallic compounds are NiAl, NiAl₃,NiTi, Ni₃Ti, CoAl, CO₃Al, TiAl, Ni₃S₁, V₅Al₆, Fe₃Al, FeAl, Ti₂P(combined addition of phosphor iron (Fe 27% P) and Ti), FeCo, FeV,Fe₂Ti, Fe₂Zr and Fe₂Nb.

Some intermetallic compounds among them have a hardness exceeding Hv 900like Si based intermetallic compounds. When using such intermetalliccompounds, it is preferable to set the lower limit of their amount to0.05 wt % similarly to the case of the ceramics based hard dispersionparticles. The amounts of the elements which constitute an NiAl basedintermetallic compound (γ′ phase, density=5.9 g/cm³) in high strengthbrass of the fourth class (Japanese Industrial standards) and itsequivalent materials are represented by:4 wt % <Al+Si<6 wt %3.5 wt % <Ni+Co+Fe<6.5 wt %.As seen from the above formulas, the high strength brass and the likecontains a composite intermetallic compound (Ni, Co, Fe)(Al, Si).Accordingly, the intermetallic compounds proposed by the invention maybe composite intermetallic compounds in which other alloy elements aredissolved in a solid state.

Such intermetallic compound phases do not have a hardness exceeding Hv900. In the case of a Cu—10 wt % Ni—3.33 wt % Si based sintered contactmaterial, the size of Ni₂Si precipitates in the particles is as small as2 μm or less and the amount of Ni₂Si precipitates is about 10% byvolume. If the amount of Ni₂Si precipitates exceeds 10% by volume, theireffect declines and therefore, the proper precipitation amount isdetermined to be 10% by volume or less. It is more preferable to use 7wt % Ni+2.33 wt % Si in an amount of 10 wt % or less, because itexhibits good sliding properties. Regarding the intermetallic compoundsand composite intermetallic compounds of the invention, it is preferableto limit the amount of the intermetallic compounds to 10% by volume orless or to limit the sum of the main elements of the intermetalliccompounds to 10 wt % or less (=about 7% by volume or less on the basisof percentage by volume). This is also effective for cost performance.

These intermetallic compounds may be added in the form of anintermetallic compound powder. Alternatively, primary powders may beadded in combination to precipitate the intermetallic compounds like thecase of Ni and Si addition.

According to the invention, it is more preferable to add theintermetallic compounds in the form of an intermetallic powder. Because,an intermetallic compound powder promotes formation of blow holes forgas escaping and prevents formation of melt-off pores, so thatdegradation of sinterability due to rapid choking of pores can beavoided.

The Fe₃Al ordered phase containing 5 wt % or more Al has a Vickershardness of 300 to 350. When adding alloy elements such as Ni and Co inan amount of 10 to 20 wt % to the above Fe₃Al ordered phase, it can behardened to a level of Hv 800 by aging treatment at about 600° C.Therefore, the Fe₃Al ordered phase has a considerable degree of freedomas a dispersion phase and is also cost effective.

(2) Selection of Ingredients for the Soft, Second Particle DispersionMaterial

While well-known solid lubricants such as MoS₂ and WS₂ may be regardedas a soft particle dispersion material, the principle of the mechanismfor improving the sliding properties by the presence of the softparticle dispersion material resides in the following point: Solidlubrication at the sliding contact surface of the sintered contactmaterial is enhanced, the sliding contact surface being in directsliding contact with the mating material while the hard particlesscratching off local agglutinates on the sliding contact surface, and asa result, attacks on the mating material are considerably reduced andseizure resistance is improved. The soft particle dispersion material isexpected to have substantially the same effect as that of thelubricating components of the friction materials described earlier. Inthe invention, the amount of the soft particle dispersion material to beadded is limited to a value much smaller than the normal amounts shownin TABLES 1, 2 and 3, that is, 1 wt % or less. The reason for this isthat if a large amount of graphite is added, the resulting sinteredlayer becomes porous as described earlier, with a transition from fluidlubrication to boundary lubrication, resulting in a high frictioncoefficient. In view of the strength of a sintered contact material, itis highly desirable that the amount of the soft, second dispersionparticles which cause a decrease in strength be markedly reduced byrestricting the amount of the hard, first non-metallic particles to anextremely small value and by employing an adequate size for the firstnon-metallic particles.

As the above soft particle material rich in solid lubricity, varioussolid lubricating materials such as shown in “Solid Lubricant Hand Book”may be used. However, it is desirable to avoid use of soft particlessuch as MoS₂ and WS₂, because they react to Cu during the sinteringprocess of the copper based sintered contact material so that MoS₂ orWS₂ is likely to be decomposed into soft copper sulfides. In addition,MOS₂ and WS₂ are very expensive. If they are used in the invention, thesurfaces of MOS₂ and WS₂ particles are coated with a reaction inhibitorsuch as water glass, or alternatively, particles granulated with waterglass etc. are added.

Graphite does not need water glass coating because it does not react toCu and Sn during sintering. However, as graphite particles become finer,they are more likely to disperse in a linked fashion within a sinteredcontact material during sintering, leading to a significant decrease instrength of the sintered compact. In such a case, it is preferable touse crushed graphite particles having a size of 0.02 mm or more orgraphite particles granulized with water glass. It has been confirmedthat when graphite is added in a large amount like the case of thefriction materials, oil film formation under high-speed sliding oillubrication is inhibited, resulting in an increased friction coefficientbecause graphite is extremely porous. Therefore, addition of graphitemore than necessary is undesirable for contact materials used in bothlow-speed and high-speed conditions like the invention.

When adding graphite in bronze based and/or lead bronze based sinteredmaterials, it is preferable to add one or more elements selected fromthe group of Ti, Cr, Mg, V, Zr, Mn, Ni and Co in order to restrain thesweating phenomenon of Sn and Pb during sintering. These elements arehighly capable of forming an intermetallic compound, reacting to Sn andPb and are excellent in affinity with respect to Sn, Pb and/or carbon.Since the sweating phenomenon of Sn and Pb is significant particularlywhere Si and Al are contained in a sintered material, it is desirable toadd one or more elements selected from the group of Ti, Cr, Mg, V, Zr,Mn, Ni and Co.

If the percentage by volume of MnS, which is added in place of Pb as aPb-less material for imparting comformability and sliding propertiessimilar to those of a lead bronze based sintered material containing 10wt % Pb, is approximate to the percentage by volume of Pb, the amount ofMns may be estimated to be about 5 wt % (the density of Mns=5.2 g/cm³and the density of Pb=11.34 g/cm³). However, a satisfactory improvementcan be obtained by 1 wt % Mns, thanks to the effect of the dispersion ofthe non-metallic hard particles.

Where a large amount of MnS is added, MnS particles disperse in a linkedfashion like graphite within the grain boundary of the sintered compact,considerably decreasing sinter strength. Therefore, the size of the MnSpowder to be added is preferably equal to or more than the size level(0.02 mm or more) of ordinary metallurgical powders. For preventing thelinked dispersion of particles such as MnS within the grain boundary,MnS is preferably alloyed beforehand at the time of production ofbronze, lead bronze and/or copper powders. The scope of the inventioncovers addition of one or more alloy elements selected from Ti, Zn, Al,Ni, Mn and others for the purpose of preventing a sulfur attack in thebronze based sintered contact material and addition of alloy elementsfor the purpose of improving other copper alloy properties.

(3) Double-layered Sintered Contact Member

The invention provides a double-layered sintered contact member formedby sinter bonding the copper based sintered contact material to an ironbased metal backing material. More specifically, according to afifteenth aspect of the invention, there is provided a double-layeredsintered contact member formed by sinter bonding any one of theabove-described copper based sintered contact materials to an iron basedmaterial.

Preferably, the double-layered sintered contact member of the inventionis formed by sinter-bonding a pressed compact formed from a sinteredcontact material containing Sn and/or Pb to an iron based material, thesintered compact sinter-bonded to the iron based material containing 0.1to 2 wt % one or more elements selected from the group consisting Cr,Si, Al, P and Ti which have higher affinity with respect to iron thanwith respect to copper and stabilize the α phase of iron more than the γphase of iron (a sixteenth aspect of the invention).

Preferably, the double-layered sintered contact member of the inventioncontains Si, Al, Ti and Cr which expand a sintered layer and/or one kindof non-metallic particles which restrains a shrinkage of a sinteredlayer, for fear that when using the double-layered sintered contactmember which has been produced through a process in which a mixed powderhaving a sintered contact material composition and containing Sn and/orPb is dispersed onto a steel plate, subjected to first sinter bonding at810° C. or more, and then subjected to second sintering by mechanicallyincreasing the density of the sintered dispersed powder layer, the layerof the mixed powder dispersed in the first sintering might peel off thesteel plate owing to sinter shrinkage (a seventeenth aspect of theinvention). In this case, Sn may be added by utilizing a Cu—Sn basedalloy powder containing Sn in an amount no less than Cu—30 wt % Snand/or an Sn primary powder so that the sintered layer in the firstsintering is expanded (an eighteenth aspect of the invention).

A method for sinter-bonding a copper based green compact to steel isdisclosed in Japanese Patent Kokai Publication No. 10-1704 (1998) filedby the present inventors. This technique teaches copper lead, bronze andlead bronze based sintered contact materials containing 0.2 to 3.0 wt %Ti, which ensure improved sinter-bondability with respect to steel andtherefore improved sliding properties.

Copper based sintered materials suffer from the problem of violent toolabrasion when machined and therefore there have been strong demands to anew selection of elements which promotes sinter bondability tocontribute to mitigation of tool abrasion.

The inventors have carefully studied the influence of various alloyelements when a green compact of a copper based sintered contactmaterial is sinter bonded to steel, and selected alloy elements whichsatisfied the following conditions:

(1) Stable sinter bondability can be ensured even for sinter bonding ofa large area such as when a sintered material is sinter bonded to thebottom face of a cylinder block for hydraulic pumps and motors(described later).

(2) Less tool abrasion occurs in machining.

The biggest problem in the above-described stable sinter bonding of abronze based powder is entrapment of various gasses generated from thesintered material. The main hindrances to sinter bonding are: (1) Gasgeneration subsequent to an emergence of a liquid phase, particularly inthe temperature range of about 700° C. or more, in the process ofincreasing density while allowing an emergence of the Cu—Sn liquidphase; (2) Swelling of a sintered compact due to entrapment of the gasgenerated by proper compaction; and (3) A compaction hindrancephenomenon caused by, for instance, choking of the Sn melt-off pores.The choking of the pores within the sintered compact caused by a suddenshrinkage during sintering can be prevented by dispersing ceramicsparticles as described earlier. In the invention, in order to attain airpermeability for coping with the rapid gas generation caused by thegeneration of a liquid phase, elements are added which exhibit strongreduction and cause expansion of a sintered compact at 700 to 850° C. atwhich the rapid liquid phase generation occurs, thereby forming airholes for the gas. More concretely, the compaction hindrance phenomenonis prevented by respectively adding the elements, Ti, Cr, Fe, FeP(phosphor iron), Si and Al. And, the amount of Sn is set to 1 to 15 wt %on the assumption that the liquid phase which affects bonding at thetime of sinter bonding is generated by addition of Sn in the form of aCu—Sn based alloy. In addition, the temperature of sinter bonding isdetermined to be equal to or more than the peritectic temperature (about800° C.) of Cu—Sn binary alloys with a view to prevent bonding defectsin sinter bonding of a sintered compact which has been compacted afterexpansion at 700° C. or more to ensure bondability.

The elements Ti, Cr, Fe, FeP (phosphor iron), Si and Al which improvesinter bondability have good affinity with respect to iron and act as aferrite generating element for steel. In addition, they function toeliminate or mitigate the transformation expandability of steel causedby cooling the steel's sintered joint surface. These features apparentlyrealize stable sinter bondability. The Sn contained in steel functionsas a ferrite generating element for steel but repels iron so that theability of Sn to diffusively penetrate into steel is insignificant andtherefore Sn does not work effectively in formation of the ferrite phaseat the sintered bonding interface. From the same point of view, Co, V,Zr etc. have the same function and are therefore included in the scopeof the invention.

Regarding addition of Ti, Cr, Si, Al etc., they may be added in the formof a primary powder or alternatively in the form of a master alloypowder or intermetallic compound powder (e.g., NiAl, NiTi, CoAl andNi₂Si) containing each of these elements.

In a double layered sintered member such as engine metals and wrappingbearings formed by dispersing a mixed powder of bronze based and/or leadbronze based sintered material onto a steel plate; sinter bonding thepower to the steel plate at 810° C. or more (first sintering); andmechanically increasing the density of the sintered dispersion layer tocarry out resintering (second sintering), the layer of the mixed powderapplied by the first sintering tends to peel off the steel plate owingto sinter shrinkage. This problem is solved by adding Si, Al, Ti, Crwhich are capable of expanding the sintered layer and/or one or morekinds of non-metallic particles (oxides, carbides, nitrides and solidlubricants) which are capable of restraining the shrinkage of thesintered layer. Thanks to this technique, the production method isapplicable to bronze based sintered contact materials that do notcontain Pb, a metal having a low melting point.

Further, the inventors have studied how to add Sn in order to restrainthe sinter shrinkage of the dispersion layer having a composition of abronze based sintered contact material and found the followingtechnique: A Cu—Sn based alloy powder at least containing Sn in anamount more than Cu—30 wt % Sn and/or an Sn primary powder are used. Thepowder which is the source of Sn is first melted in the first sintering,reacting to the surrounding Cu and/or the Cu—Sn based alloy powdercontaining 12 wt % or less Sn, whereby the sintered dispersion layer isexpanded while forming β, γ, ζ, δ, ε and η phases (see the Hansen'sCu—Sn binary phase diagram). Thus, sinter bondability is moreeffectively achieved.

BRIEF EXPLANATION OF THE DRAWINGS

FIG. 1 shows a shape of a compact used as a tensile test specimen.

FIG. 2 is a graph showing the results of tests conducted for checkingthe tensile strength of CuNiSi and CuSnNiSi sintered materials.

FIGS. 3(a), (b), (c) and (d) are photographs showing the metallographicstructures of Cu—Ni—Si based sintered compacts.

FIG. 4 is a photograph showing the metallographic structure of aCu-3Ni-1Si-0.5SiO₂ based sintered compact.

FIG. 5 shows a shape of a specimen for constant rate friction abrasiontests.

FIG. 6 shows a photograph of the metallographic structure of aCu-10Sn-10Ni-0.55FeP-3Pb (B16) sintered compact.

FIG. 7 shows a shape of a specimen for sinter bonding tests.

FIG. 8 shows shapes of a cylinder block and a valve plate used in adurability test.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to the drawings, examples of the copper based sinteredcontact material and double layered sintered contact member of theinvention will be concretely described below.

EXAMPLE 1

The mixed powders shown in TABLE 4 were prepared using an electrolyticCu powder (CE25, CE15); Si, TiH powders of #300 mesh or less; phosphoriron (Fe 25 wt % P); NiAl₃; Ni, Fe powders having an average particlediameter of 5 μm; an Fe 48 wt % Co powder having an average particlediameter of 9.8 μm; an SiO₂ powder having an average diameter of 21 μm;a zircon sand (ZrO₂ SiO₂) powder having an average particle diameter of23 μm; Al₂O₃ powders having average particle diameters of 2 μm and 24μm, respectively; a ZrB₂ powder having an average particle diameter of 1μm; a W, Mo, TiN powder; an MnS powder having an average particlediameter of 1.2 μm; and an artificial graphite (SGO) powder having anaverage particle diameter of 50 μm. These mixed powders were pressed ata compacting pressure of 2 to 5 ton/cm², thereby forming green compacts.The green compacts thus formed were respectively sintered in anatmosphere of Ax gas (ammonia cracked gas) having a dew point of 35° C.or less. It should be noted that the CuNiSi ternary sintered compactsshown in TABLE 4 were respectively prepared with an Ni to Si weightratio of 3:1 and allowed to have high strength by precipitation of anNi₂Si based intermetallic compound. For checking strength aftersintering, the mixed powders were respectively subjected to compactionand sintering to form tensile test specimens having the shape shown inFIG. 1. With these test specimens, tensile tests were conducted.

TABLE 4 No. CE25 Ni Si ZrB₂ Al₂O₃—1 Al₂O₃—2 FeP SGO MnS Mo A1 Bal. 1.50.5 A2 Bal. 1.5 0.5 0.3 A3 Bal. 1.5 0.5 0.3 A4 Bal. 1.5 0.5 0.3 A5 Bal.1.5 0.5 1.5 A6 Bal. 1.5 0.5 0.3 1.5 A7 Bal. 1.5 0.5 0.3 1.5 A8 Bal. 1.50.5 0.3 0.75 A9 Bal. 1.5 0.5 0.3 1 A10 Bal. 1.5 0.5 0.3 1.5 0.75 A11Bal. 1.5 0.5 0.3 1.5 1 A12 Bal. 2.25 0.75 A13 Bal. 2.25 0.75 0.3 A14Bal. 3 1 A15 Bal. 3 1 0.3 A16 Bal. 3 1 0.5 A17 Bal. 3 1 0.7 A18 Bal. 3 10.5 A19 Bal. 3 1 1 A20 Bal. 3 1 2 A21 Bal. 3 1 A22 Bal. 3 1 A23 Bal. 3 1A24 Bal. 3 1 A25 Bal. 3 1.75 A26 Bal. 3 A27 Bal. 3 1 A28 Bal. 4.5 1.5A29 Bal. 6 2 A30 Bal. 10 3.33 A31 Bal. 10 3.33 A32 Bal. 10 3.33 A33 Bal.4.5 A34 Bal. 2 A35 Bal. 3 1 A36 Bal. 3 1 A37 Bal. 3 1 COMPARATIVE P31CEXAMPLE 1 COMPARATIVE Al₂O₃ EXAMPLE 2 COMPARATIVE ZrO₂ EXAMPLE 3COMPARATIVE SiO₂ EXAMPLE 4 COMPARATIVE SiC EXAMPLE 5 COMPARATIVE Si₃N₄EXAMPLE 6 PV No. W SiO₂ FeCo Fe TiH NiAl₃ ZrO₂SiO₂ TiN VALUE Δ Wmm A13000 0.19 A2 1500 0.15 A3 4000 0.02 A4 1500 0.19 A5 4000 0.08 A6 35000.13 A7 3000 0.32 A8 4000 0.02 A9 4500 0.01 A10 1000 0.02 A11 2000 0.02A12 4000 0.082 A13 3000 0.14 A14 4500 0.09 A15 3000 0.12 A16 5000 0.04A17 3000 0.11 A18 2500 0.16 A19 6000 0.1 A20 7000 0.12 A21 1 6000 0.09A22 2 5500 0.07 A23 0.5 6000 0.02 A24 1 4000 0.045 A25 1.5 6500 0.09 A261 5000 0.08 A27 5 7000 0.13 A28 6000 0.214 A29 7000 0.265 A30 5000 0.392A31 1 4000 0.241 A32 0.5 4000 0.075 A33 1.5 6500 0.06 A34 3 6000 0.06A35 0.5 4500 0.07 A36 1 5000 0.042 A37 0.5 7000 0.052 COMPARATIVE 50000.361 EXAMPLE 1 COMPARATIVE 1600 — EXAMPLE 2 COMPARATIVE 2400 — EXAMPLE3 COMPARATIVE 3600 — EXAMPLE 4 COMPARATIVE 3200 — EXAMPLE 5 COMPARATIVE2800 — EXAMPLE 6

FIG. 2 shows the results of the tensile tests. It will be understoodfrom the graph of FIG. 2 that the maximum sinter strength (tensilestrength) can be obtained by about 4 wt % (Ni+Si). However, if theamount of (Ni+Si) exceeds 4 wt %, fine Ni₂Si compounds precipitate inthe sintered material as shown in the structural photographs of FIG. 3,and as the amount of (Ni+Si) increases, larger intermetallic compoundsprecipitate in the grain boundary, resulting in a decrease in strength.As seen from FIG. 2 and TABLE 4, a significant decrease in strength wasnot observed when adding hard particles such as ZrO₂, SiO₂, Al₂O₃−1,phosphor iron (Fe 25P), Fe, Mo and W in amounts of about 2 wt % or less.It can be understood from the comparison between No. A3 and No. A9 andbetween No. A7 and No. A11 in TABLE 4 that the significant decrease ofstrength when soft MnS (density=5.23; quantity=1.7% by volume) is addedis a very serious problem. It can however be understood from thecomparison between No. A3 and No. A8 and between No. A7 and No. A10 inTABLE 4 that even though soft particles are used, a drop in strength canbe reduced where graphite (SGO) having an average particle diameter of50 μm is added in an amount of 0.75 wt % (density=2.0; quantity=3.3% byvolume). Therefore, it is apparent that use of coarse particles (e.g.,granules) is desirable for MnS.

FIG. 4 shows a structural photograph of a sintered compact of the powderNo. 23 shown in TABLE 4. SiO₂ particles having a particle diameter of 10μm or less are dispersed, being entrapped within the matrix due to theshift of the grain boundary during sintering, whereas most of SiO₂particles having a size of more than 10 μm are dispersed within thegrain boundary. Therefore, it is obvious that a decrease in the strengthof the sintered compact can be restrained by adjusting most of SiO₂particles to 10 μm or less. Apparently, CuNiTi, CuTiSi and CuNiAl basedmaterials may be used as a high-strength copper based sintered materialsimilar to the above-described CuNiSi based material. In this case, theNi to Ti ratio, Ti to Si ratio and Ni to Al ratio are preferably withinthe range of from 4:1 to 3:1.

Next, constant rate friction abrasion tests were conducted using slidingtest specimens such as shown in FIG. 5 in order to check the slidingproperties of the copper based sintered materials. Specifically, the PVvalue representative of the product of a pressing force (kgf/cm²) andsliding speed (m/sec) at the time when a friction coefficient rapidlyincreases or when a sudden abnormal wear occurs and the wear amount ΔW(mm) of each test specimen at that time were measured. The results ofthe tests are also shown in TABLE 4. The test condition is as follows:As a mating material for each specimen, SCM420 was used, which had beensubjected to thermal treatment of carburizing, quenching and temperingsuch that its surface had a Rockwell hardness of HRC 60. While the #10lubricant having a temperature of 80° C. being supplied at a rate of 100cc/min, the mating material is rotated with the sliding speed being 10m/sec. Under this condition, each specimen was tested for ten minutesand this test was repeated until the limit the specimen can withstandwas reached. Then, the PV value inherent to the contact material and thewear amount of the specimen were measured.

It has been found from the comparison among the sliding properties (PVvalues) of the CuNiSi ternary materials (Nos. A1, A12, A14 and A28 toA30) that the PV values start to be improved to a considerable extentfrom the point where Ni+Si=4 wt %; achieve their maximum improvement atthe point where Ni+Si=9.33 wt %; and start to drop after the point whereNi+Si=9.33 wt %. As seen from the sintered compact structures shown inFIG. 3, this change is attributable to the fact that when Ni and Si areadded in an amount of 4 wt % or more, an extremely fine NiSiintermetallic compound starts to precipitate within the sinteredcompact, leading to a considerable improvement in the PV value and whenNi and Si are added in an amount of 13.3 wt %, an extremely coarseintermetallic compound precipitates within the grain boundary leading toa decrease in the PV value. It is also understood that since the volumepercentage of the intermetallic compound is 100% when Ni+Si=100 wt %,Ni+Si=13.33 can be approximated by about 10% by volume and, therefore,the volume of the dispersed NiSi based intermetallic compound ispreferably 10% by volume or less. Further, Ni+Si is preferably used inan amount of 6% by volume which is equivalent to Ni+Si=9.33 wt % becausewith this amount, a large amount of a coarse intermetallic compound doesnot precipitate.

It was found from an investigation on the effect of Al₂O₃ serving as thehard particles that addition of fine Al₂O₃ (Al₂O₃−1) prevents a drop inthe PV value and improves wear resistance, whereas addition of Al₂O₃(Al₂O₃−1) in an amount of 0.5 wt % or more leads to a drop in the PVvalue. When coarse Al₂O₃ (Al₂O₃−2) was added in an amount of 0.3 wt %, asignificant drop in the PV value was observed. A considerableimprovement was observed in both the PV value and wear resistance in thecoexistence of Al₂O₃−1 and a solid lubricant such as graphite (SGO) orMnS.

The effect of addition of SiO₂ particles and ZrO₂ SiO₂ was observed inthe powders Nos. A23, A24, A35 and A36. Concretely, even when they werecoarse particles, the PV value and wear resistance could be improvedwhen the amount of these particles was up to 1.0 wt %, and particularlythe improvement achieved by addition of SiO₂ was significant when itsamount was 0.5 wt %. In addition, virtually no attacks on the matingmaterial was detected even when they were coarse particles.

It was confirmed by the powder No. A37 that addition of TiN particleshad the effect of considerably improving the sliding properties.

The considerable PV value improving effect of Mo, W, Fe addition wasconfirmed by the powders No. A19 to A22 and A25. Since the metallicparticles of Mo and W are originally not hard particles, they have alittle effect of improving wear resistance. Part of the metallicparticles of Fe reacts to Si contained in a CuNiSi based material,thereby forming a hard FeSi based intermetallic compound so that wearresistance is improved. In the powder No. A27, an FeCo ordered alloypowder is used in place of Fe and substantially the same degree ofimprovement in the PV value and wear resistance has been confirmed. Itis also apparent that where a hard martensitic Fe—C alloy is dispersed,a considerable improvement in wear resistance can be expected.

The test results of the CuNiTi and CuNiAl based materials (Nos. A26, A33and A34) serving as a high-strength copper based sintered materialsimilar to the CuNiSi based material are shown and proved to haveexcellent sliding properties similar to those of the CuNiSi basedmaterial.

As a comparative example for the high-strength contact materials, thesliding properties of P31C (Comparative Example 1:Cu-28Zn-3Ni-4Al-1Si-0.7Fe-0.6Co) are shown. P31C is a high-strength castmaterial having excellent wear resistance and containing a large amountof an intermetallic compound within a hard matrix comprised of α and βphases. It is understood that the high-strength copper based sinteredcontact materials of the invention have much better properties than thiscomparative material. The result of EPMA (analysis by use of an X-raymicro analyzer) conducted on the intermetallic compound dispersing inComparative Example 1 is shown in TABLE 5. The intermetallic compound(Ni, Co, Fe)(Al, Si) within the P31C material is a compositeintermetallic compound in which two kinds of intermetallic compounds,i.e., Al rich and Si rich intermetallic compounds are dispersed. Ni isrich in the Al rich intermetallic compound, whereas Fe and Co are richin the Si rich intermetallic compound.

TABLE 5 The chemical composition of the intermetallic compounddispersing in the annealed structure of P31C (mol %) Ni Co Fe Cu Al SiZn 22.6 14.7 15.8 6.5 22.4 15.2 2.8 31.6 9.06 6.16 8.87 31.4 9.13 3.76

It is assumed from the result that the poor wear resistance ofComparative Example 1 is attributable to the likelihood that the matrixof P31C agglutinates, while the excellent wear resistance of thesintered contact material of the invention is attributable to thepresence of oil impregnated pores although the number of pores is small.

An investigation was also conducted to check the sliding properties ofeach of ceramics materials such as Al₂O₃ (Comparative Example 2), ZrO₂(Comparative Example 3), SiO₂ (Comparative Example 4), SiC (ComparativeExample 5), and Si₃N₄ (Comparative Example 6). In this investigation,each sliding test specimen was finished so as to have a surfaceroughness of Rmax=1 μm or less. As seen from TABLE 4, their slidingproperties were not as good as they were expected under a high slidingspeed condition (10 m/sec), but the higher thermal shock resistance, thebetter sliding properties. Among them, Al₂O₃ revealed the disadvantagesthat its surface roughness Rmax after the sliding test was as high as 5to 15 μm, that chipping due to thermal shocks was clearly found on thesliding contact surface, and that it forcefully attacked on its matingmaterial. However, it was found that seizure did not occur at a maximumsurface pressure of 800 kgf/cm² and the Al₂O₃ material could slide witha low friction coefficient on condition that the Al₂O₃ material slid ata sliding speed of 2.5 m/sec or less and is not subjected to a loadcaused by thermal shocks because of local agglutination.

EXAMPLE 2

This example is associated with an investigation conducted on Cu—Snbronze based sintered contact materials to which lead is added inamounts up to 3 wt %. The sintered contact materials used in thisexample were produced in the following way: The mixed powders shown inTABLE 6 were prepared using, in addition to the raw powder materialsused in Example 1, Sn, Pb, Al, cemented carbide and Cu—30 wt % Zn whichhave a size of #250-mesh or less and Cr, Mn, MnSi, TiSi which have asize of #300-mesh or less. These powders were compacted at a compactingpressure of 2 ton/cm² to form green compacts and then, the greencompacts were respectively sintered in an atmosphere of AX gas (ammoniacracked gas) having a dew point of 35° C. or less. The sinteringtemperature varied depending on the compositions of the materials butranged from 850 to 900° C. The sliding properties (PV value, ΔW)evaluated in the same way as in Example 1 are shown in TABLE 6.

TABLE 6 CEMENTED PV No. CE15 Sn Pb FeP TiH Ni Si Al Zn SiO₂ NiAl₃ Mn FeCo MnSi TiSi CARBIDE Cr VALUE Δ Wmm B1 Bal. 10 0 5000 0.19 B2 Bal. 10 30 8000 0.24 B3 Bal. 10 3 0.55 8000 0.09 B4 Bal. 10 3 1.5 6500 0.02 B5Bal. 10 3 3 3000 0.08 B6 Bal. 10 3 2 8000 0.05 B7 Bal. 10 3 1.5 2 75000.01 B8 Bal. 10 3 3 2 4500 0.06 B9 Bal. 10 3 0.65 2.4 5500 0.03 B10 Bal.10 3 1.1 0.4 5000 0.02 B11 Bal. 10 3 3 1.1 0.4 3500 0.09 B12 Bal. 10 3 32 6500 0.08 B13 Bal. 10 3 3 3 1 4000 0.03 B14 Bal. 10 3 3 1 8000 0.09B15 Bal. 10 3 4.5 1.5 7000 0.17 B16 Bal. 10 3 0.55 10 6000 0.04 B17 Bal.10 3 0.55 20 4500 0.08 B18 Bal. 5 3 0.55 15 5500 0.08 B19 Bal. 5 3 3 115 6000 0.06 B20 Bal. 5 3 0.55 21 6000 0.06 B21 Bal. 5 3 3 1 21 85000.02 B22 Bal. 14 3 0.55 7000 0.11 B23 Bal. 16 3 0.55 6000 0.09 B24 Bal.10 3 0.55 0.3 7000 0.01 B25 Bal. 10 3 1.5 7000 0.02 B26 Bal. 10 3 3 75000.02 B27 Bal. 10 3 1 3 3500 0.11 B28 Bal. 10 3 2 2 7000 0.05 B29 Bal. 103 1 4000 0.13 B30 Bal. 10 3 1 6500 0.11 B31 Bal. 10 3 5 5500 0.06 B32Bal. 10 3 1 5 8500 0.02 B33 Bal. 10 3 1 5 7500 0.04 B34 Bal. 10 3 1 75000.12 COMPARA- PBC 5000 0.21 TIVE EXAMPLE 1 COMPARA- LBC 5500 0.39 TIVEEXAMPLE 2

It is understood from the tests conducted on the powders Nos. B1 to B5shown in TABLE 6 that when the amount of phosphor iron is up to 1.5 wt%, the PV value is slightly improved with a considerable improvement inwear resistance, but when the amount of phosphor iron is 3 wt %, the PVvalue greatly decreases. Accordingly, the proper amount of phosphor ironadded is less than 3 wt % and more preferably about 2 wt %.

The powders Nos. B6 to B8 shown in TABLE 6 were used for checking theeffect of addition of phosphor iron. It was found that single additionof Ti gave the effect of promoting sinterability while allowingdispersion of fine Pb and that Ti took nitrogen from an AX gasatmosphere and carbon from an organic lubricant (0.7 wt % Acra Wax)which had been added to the mixed powder so that slight amounts of TiNand TiC were produced, contributing to achievement of improved wearresistance without degrading slidability. In the coexistence of Ti andphosphor iron, most of Ti precipitates as TiP or Ti₂P. In the mixedpowder No. B7, substantially all the amount of P contained in phosphoriron reacted to produce Ti₂P while the remaining Ti dispersing withinthe sintered compact as Fe₂Ti, bringing about a considerable improvementin the PV value and wear resistance. The degradation of the slidingperformance of the material No. 8 is apparently attributable to thepresence of excessive phosphor iron.

The powders Nos. B9 to B15 were prepared from combinations of thehigh-strength elements which were studied in Example 1. It was foundthat addition of Ni in a high concentration created an eutectoidstructure composed of an Ni—Sn based intermetallic compound such asshown in FIG. 6; considerably increased sintered compact hardness (aboutHv=200); and markedly improved wear resistance rather than the PV value.In addition, it was found that a significant improvement in the PV valueand wear resistance was not achieved by addition of Zn in a highconcentration.

The powders Nos. B22 and B23 were prepared by dispersing a Cu—Snintermetallic compound in a sintered contact material and an apparentimprovement in the PV value was observed in these specimens. The powdersNos. B 24 to B34 were prepared by dispersing SiO₂, NiAl₃, MnSi, FeCo,TiSi, cemented carbide and Cr respectively. Except MnSi, an improvementin the PV value or wear resistance was observed.

EXAMPLE 3

This example is associated an investigation conducted on bronze basedand lead bronze based sintered contact materials to which lead is addedin amounts up to 25 wt %. The sintered contact materials used in thisexample were produced in the following way: The mixed powders shown inTABLES 7 and 8 were prepared using, in addition to the raw powdermaterials used in Example 1 and Example 2, KJ4 (25 wt % P—Cu alloy) of#250-mesh or less. These powders were compacted at a compacting pressureof 2 ton/cm² to form green compacts and then, the green compacts wererespectively sintered in an atmosphere of AX gas (ammonia cracked gas)having a dew point of 35° C. or less. The sintering temperature varieddepending on the compositions of the materials but ranged from 800 to860° C.

TABLE 7 CE15 3.18 gr/cm³ No. Cu Sn Pb TiH Ni Si SiO₂ FeP Mo W NiAl₃ FeCo CaF₂ PV VALUE Δ Wmm C1 Bal. 11 1 0.15 5500 0.08 C2 Bal. 11 3 0.156000 0.06 C3 Bal. 11 5 0.15 6000 0.09 C4 Bal. 11 8 0.15 6000 0.13 C5Bal. 11 10 0.15 5500 0.27 C6 Bal. 11 10 1 2 7500 0.04 C7 Bal. 11 10 3 17500 0.05 C8 Bal. 11 10 0.3 8000 0.03 C9 Bal. 11 10 1 6500 0.03 C10 Bal.11 10 2 6000 0.08 C11 Bal. 11 10 1 2 8000 0.02 C12 Bal. 11 10 2 55000.08 C13 Bal. 11 10 0.55 2 7500 0.04 C14 Bal. 11 10 1.5 8000 0.04 C15Bal. 11 10 3 7000 0.03 C16 Bal. 11 10 2 2 8000 0.03 C17 Bal. 11 10 17500 0.05 COMPARATIVE LBC 5500 0.358 EXAMPLE 2

TABLE 8 PV No. Cu Sn Pb Mo W SiO₂ FeP VALUE Δ Wmm D1 Bal. 0 25 5000* >1.2 D2 Bal. 0 25 2 7000 0.72 D3 Bal. 0 25 4 7500 0.61 D4 Bal. 025 2 6500 0.75 D5 Bal. 0 25 4 7500 0.5 D6 Bal. 0 25 0.3 7500 0.37 D7Bal. 0 25 0.5 7000 0.27 D8 Bal. 0 25 1 6500 0.18 D9 Bal. 0 25 0.55 65000.46  D10 Bal. 0 25 1.5 7500 0.21 *A limit at which abnormal wearoccurs.

The materials Nos. C1 to C5 were used to check the effect of Pb additionon Cu-11Sn. Apparently, Pb provides excellent PV value reproducibilityrather than an improved PV value, but significantly degrades wearresistance. Where any one of Fe+Ti (Fe₂Ti), Ni+Si (NiSi intermetalliccompounds), SiO₂, phosphor iron, Mo, W, NiAl₃ and FeCo is added inaddition to Pb, considerably improved wear resistance and, inconsequence, an improved PV value can be achieved. It is understoodparticularly from the test results of the material Nos. C10 to C13 thatimproved wear resistance and an improved PV value can be ensured in thecoexistence of Mo or W metallic particles and hard particles such asphosphor iron rather than in the single presence of Mo or W metallicparticles. Accordingly, the PV value improving effect of Mo and Wmetallic particles can be achieved when they respectively coexist withthe hard non-metallic particles.

Regarding the sintered contact materials containing KJ4 shown in TABLE8, the PV values and wear resistance of the materials containing otherpowders in addition to KJ4 are superior to those of the material No. D1to which KJ4 is added alone. The reason for this is that the materialNo. D1 has very poor wear resistance and is susceptible to abnormal wearbefore seizing. Although the material No. D8 to which 1 wt % SiO₂ isadded has much better properties than the material No. D1, SiO₂ additionon the quantitative level of the specimen No. D8 causes an emergence ofthe mating material-attack property. Accordingly, it is preferable tolimit the amount of SiO₂ to less than 1.0 wt %.

When making comparison between the materials shown in TABLE 7 and thematerials shown in TABLE 8, it is understood that the sintered materialsmade of the powders shown in TABLE 8 and having higher hardness achievemore significant improving effect. This clearly indicates that the forceof peeling agglutinates by particle dispersion is insufficient in thecase of soft sintered materials.

EXAMPLE 4

This example discusses a method of producing a double-layered sinteredcontact member in which a bronze based sintered contact materialcontaining no lead is integrated with a steel plate (SPCC) serving as ametal backing. The sintered contact materials used in this example wereprepared from the mixed powders shown in TABLE 9 which contained, inaddition to the raw powder materials used in Examples 1, 2 and 3, Cu—10wt % Sn, Cu—20 wt % Sn and Cu—33 wt % Sn which had a size of #250 meshor less. Each copper based sintered powder material was dispersed onto a3.5 mm thick metal backing such that the finished product had athickness of 0.6 mm. This composite material was sintered at 820 to 860°C. in an RX gas atmosphere, rolled by a roller such that the thicknessof the overall resulting sintered layer was 0.8 mm and then sinteredagain at 800 to 840° C. TABLE 9 shows cases where the copper basedsintered material layer was not sinter-bonded but peeled off during thefirst sintering process or peeled off during the rolling process. It isunderstood from TABLE 9 that a considerable shrinkage occurred,accompanied with peeling of the copper based sintered material layerfrom the metal backing at the sintering temperature in the materialsNos. F1 and F2 prepared from only an alloy powder and the material No.F3 prepared from a copper powder and Cu20Sn alloy powder. As understoodfrom the materials Nos. F4 to F7, sinter bonding was observed where apowder having an Sn concentration equal to or more than Cu33Sn was used.The reason for this is as follows: In the temperature zone equal to orlower than the peritectic temperature (about 800° C.) of Cu—Sn alloybased materials, Cu33Sn or Sn melts during sintering, generating liquidphases essential for sinter bonding. These liquid phases start to reactto the Cu powder so that various CuSn intermetallic compounds such as β,γ, ζ, δ and ε are formed. The expansion at the time of the formation ofthe CuSn intermetallic compounds hampers the shrinkage of the sinteredmaterial layer which is the cause of the peeling-off.

TABLE 9 SINTER Cu10Sn Cu14Sn Cu Cu20Sn Cu33Sn Sn Cu10Sn10Pb SiO₂—2 Si₃N₄CaF₂ SGO Cu40Al NiAl₃ Cr BONDABILITY F1  100 X F2  100 X F3  Bal. 50 XF4  Bal. 31 Δ2/5 F5  Bal. 8 ◯0/5 F6  Bal. 11 0.5 ◯0/5 F7  Bal. 14 ◯0/5F8  100 Δ2/5 F9  Bal. 0.5 ◯ F10 Bal. 0.5 X5/5 F11 Bal. 31 0.5 ◯ F12 Bal.4 Δ2/5 F13 Bal. 4 0.5 ◯ F14 Bal. 4 0.5 ◯ F15 Bal. 2 1 ◯ F16 Bal. 2 1 ◯F17 Bal. 2 1 1 ◯ F18 Bal. 1 ◯ F19 Bal. 2 ◯ F20 Bal. 31 0.5 1 ◯ F21 Bal.31 0.3 1 ◯ F22 Bal. 31 0.5 1 ◯

In view of the above fact, it is very effective to add elements whichactively hamper the shrinkage of the copper based sintered materiallayer. It is also desirable to add SiO₂, Si₃N₄, graphite and the likewhich retard the shrinkage of the sintered material layer or elementssuch as Al, Si, Ti and Cr which actively impart expandability. Singleaddition of Al or Si causes vigorous reaction to the atmosphere so thatthey are preferably added in alloy or intermetallic compound form. Whenadding Al, Si, Ti or Cr in the form of primary powder, the sinteringatmosphere is preferably a good non-oxidized atmosphere such as AX gasatmosphere or vacuum atmosphere.

In the materials Nos. F8, F9 which are LBC bronze (Cu10Sn10Pb), Pbhaving a low melting point is contained in large amounts so that sinterbondability is ensured. However, the actual range of sinteringtemperature for the composition of the powder No. F8 is generally 780 to810° C. and the control especially in the vicinity of the peritectictemperature (800° C.) is difficult, so that the atmosphere and theoxidation of the powder must be strictly controlled. In this example,the powders Nos. F8 and F9 were sinter bonded at 820° C. and peeling dueto a considerable shrinkage occurred in the case of the powder No. 8. Itis obvious from the result that a significant improvement can beachieved by addition of the aforesaid sinter inhibitors (e.g., Si₃N₄)and expansion elements.

Each double-layered sintered contact member formed by sinter bonding asintered material to a metal backing was rounded so as to have an innerdiameter of 50 mm and an investigation was conducted to check peeling ofthe sintered layer from the metal backing and occurrence of cracking.Good results were obtained in all the members. Further, occurrence ofpeeling of the sintered layer and cracking was checked after burnishingtreatment subsequent to welding of the metal backing portion. As aresult, it was found that a sound wrapping bearing could be producedfrom all the members.

EXAMPLE 5

In this example, tests were conducted by respectively sinter bonding theabove-described sintered contact materials to a steel (SCM440H) havingthe shape shown in FIG. 7. The sinter contact materials for bonding usedas specimens were prepared by compacting the mixed powders shown inTABLE 10 at a compacting pressure of 2 ton/cm², the mixed powders beingprepared from the raw powder materials described in Examples 1 to 4.Sinter bonding temperatures for the materials Nos. E1 to E17 and for thematerials Nos. E18 and E19 in TABLE 10 were 860° C. and 1,070° C.respectively. After sinter bonding, the bonded area percentage(bondability) of each specimen was checked by use of an ultrasonictester. The test results are also shown in TABLE 10.

TABLE 10 No. Cu Sn Pb Ti Cr V FeP Ni Mo SiO₂ NiAl₃ Ni₃Si CaF₂ SiBONDABILITY E1 Bal. 10 10 2 73.0% E2 Bal. 10 10 0.5 97.0% E3 Bal. 10 100.5 1 2 98.5% E4 Bal. 10 10 0.5 2 97.0% E5 Bal. 10 10 0.1 2 91.0% E6Bal. 10 10 0.5 2 97.0% E7 Bal. 10 10 0.5 1 2 98.0% E8 Bal. 14 5 2 63.0%E9 Bal. 14 5 0.5 2 0.3 91.0% E10 Bal. 16 0 0.5 2 94.0% E11 Bal. 10 100.5 1.5 99.5% E12 Bal. 10 10 0.5 1 1.5 99.0% E13 Bal. 10 10 0.5 0.5 1.599.5% E14 Bal. 10 10 0.5 0.3 3 99.5% E15 Bal. 10 10 0.5 1 2 98.0% E16Bal. 10 10 0.5 2 95.0% E17 Bal. 10 10 0.5 0.5 99.0% E18 Bal. 6 0.3 287.5% E19 Bal. 1 6 0.3 2 96.5% COMPARATIVE Bal. 11 10 2 CASTING EXAMPLE4*

It is understood from the test results of the materials Nos. E1, E2, E5,E6 and E16 that a considerable improvement in sinter bondability can beachieved by addition of small amounts of Ti, Cr and V and also achievedby addition of phosphor iron, SiO₂ and CaF₂. Addition of Si and Al whichare the expansion elements of Ni₃Si and NiAl₃ considerably improvesbondability by their venting effect exerted in the course of sintering.Phosphor iron, Si and Al are extremely desirable elements, because theyhave higher affinity with respect to steel than with respect to copperand stabilize the ferrite phase of iron so that the ferrite phase havinga width of 20 μm or more is substantially uniformly formed on thebonding interface at the steel side and the peeling force imposed on thebonding interface by transformation-induced expansion in the coolingprocess after sinter bonding can be reduced to a great extent.

The chief components of the liquid phases emerging during sinter bondingare Sn and Pb. In this example, it has been found that even if Pb is notadded, sound sinter bondability can be achieved by addition of smallamounts of Cr, Si, Ti, phosphor iron etc. In the materials Nos. E18 andE19 which are sinter bondable in a high temperature zone, 1 wt % Snsignificantly contributes to an improvement in bondability. In view ofthis and the percentage of bonded area, addition of Sn in an amount of 1wt % or more is desirable.

EXAMPLE 6

In this example, the typical sintered contact materials described inExample 5 were respectively sinter bonded to the bottom face P of acylinder block of a hydraulic pump (“HPV95” produced by KomatsuLimited.) and incorporated into a hydraulic pump. Then, a durabilitytest was conducted in a real condition. A lead bronze based sinteredcontact material having a composition of Cu—10 wt % Sn—1 wt % Ti—2 wt %NiAl₃−5 wt % Pb—1 wt % FeP (phosphor iron) was sinter bonded to theinner circumference of the bore Q of the cylinder block used in thedurability test.

The durability test was conducted for up to 300 hours with a rotationalspeed of 2,300 rpm and discharged hydraulic pressure of 420 kg/cm². Avalve plate which served as the mating member for the cylinder blockbottom face was prepared by carburizing an SCM420H material and thenapplying the mutual rubbing rapping treatment to the SCM420H material aswell as to the cylinder block bottom face. Assuming that the cylinderblock had already been used for a long time, the curvature of the bottomface was adjusted by the mutual rubbing rapping treatment such that therelationship between the contact rates of three sealed portions A, B, C(see FIG. 8) in the valve plate relative to the cylinder block wasapproximately represented by A:B:C=1:1:0.2 and such that the cylinderblock could whirl centrifugally during the durability test. Afterelapses of 50 hours, 100 hours and 300 hours in the test, the seizure ofthe bore of the cylinder block, the seizure and wear amount of thebottom face and the seizure and wear amount of the valve plate weremeasured. The result is shown in TABLE 11.

TABLE 11 TEST BOTTOM WEAR TIME FACE AMOUNT WEAR (hr) SEIZURE (μm) AMOUNT(μm) E2 50 x 17 5 E3 50 ∘ 5 4 100 x 7 6 E4 50 x 14 3 E6 50 ∘ 7 3 100 x16 4 50 ∘ 5 2 E7 100 ∘ 6 3 300 ∘ 9 6 50 ∘ 9 3 E10 100 ∘ 12 6 300 ∘ 18 950 ∘ 5 3 E11 100 ∘ 7 4 300 x 12 8 50 ∘ 5 3 E12 100 ∘ 6 5 300 ∘ 9 8 50 ∘2 5 E13 100 ∘ 3 9 300 ∘ 5 15 COMPARATIVE 50 ∘ 14 3 EXAMPLE 4 100 x 26 5

It is understood from the result that the contact materials of theinvention containing the non-metallic particles have durability superiorto that of Comparative Example 4 and the materials Nos. E2 and E4. Animprovement in wear resistance by dispersion of the hard particles isessential, particularly, in a high-speed sliding condition accompaniedwith vibration. For instance, it is understood from a comparison betweenthe materials Nos. E4, E6 and E7 that both seizure resistance and wearresistance are markedly improved by the coexistence of Mo and thenon-metallic particles. It is also understood from the material No. E13that addition of SiO₂ contributes to an improvement in wear resistancewhile slightly increasing the mating material-attack property. Takingthis into account, it is necessary to properly control the amount ofSiO₂.

1. A copper based sintered contact material wherein non-metallicparticles, comprised of one or more substances selected from the groupconsisting of oxides, carbides, nitrides and carbonitrides, have anaverage particle diameter of 45 μm or less and are dispersed in anamount ranging from 0.2% by volume or more to less than 4% by volume. 2.The copper based sintered contact material according to claim 1, whereinsaid oxides are thermal-shock-resistant, oxide-based ceramics comprisingSiO₂ and/or one or two or more elements selected from the groupconsisting of Si, Al, Li, Ti, Mg and Zr.
 3. The copper based sinteredcontact material according to claim 1, wherein said carbides, nitridesand carbonitrides comprise one or more substances selected from thegroup consisting of the carbides, nitrides and carbonitrides of W, Ti,Mo and V and/or cermet particles produced by sintering said substanceswith Co and/or Ni.
 4. The copper based sintered contact materialaccording to claim 1 or 2, wherein said non-metallic particles are inthe form of granules and/or fibers.
 5. The copper based sintered contactmaterial according to any one of claims 1 to 3, wherein one or moremetals and/or alloy particles selected from the group consisting of Mo,W, Cr, Go, Fe and Fe—C are dispersed in an amount of 0.5 to 5.0 wt %. 6.The copper based sintered contact material according to any one ofclaims 1 to 3, containing 1 wt % or less MnS and/or 1 wt % or lessgraphite.
 7. The copper based sintered contact material according to anyone of claims 1 to 3, containing 1 wt % or less MnS and/or 1 wt % orless graphite, wherein the average particle diameter of said MnS and/orgraphite ranges from 20 to 200 μm or less.
 8. The copper based sinteredcontact material according to any one of claims 1 to 3, containing atleast 1 to 16 wt % Sn and 0 to 25 wt % Pb.
 9. The copper based sinteredcontact material according to any one of claims 1 to 3, furthercontaining 12 to 16 wt % Sn and a Cu—Sn compound phase which isdispersedly precipitated in the structure thereof.
 10. The copper basedsintered contact material according to any one of claims 1 to 3,containing at least 1 to 16 wt % Sn and 0 to 25 wt % Pb, furthercontaining one or more alloy elements selected from the group consistingof Zn, Mn, Be, Mg, Ag, and Bi, and a solid lubricant such asMoS_(2, CaF) ₂ and WS₂.
 11. A double-layered sintered contact memberproduced by sinter bonding the copper based sintered contact material ofany one of claims 1 to 3 to an iron based material.
 12. A double-layeredsintered contact member, which is produced by sinter bonding a pressedcompact, formed from a sintered copper based contact material of any oneof claims 1 to 3 and further containing Sn and/or Pb, to an iron basedmaterial, and wherein the sintered compact sinter bonded to the ironbased material contains 0.1 to 2 wt % one or more elements selected fromthe group consisting of Cr, Si, Al, P and Ti which have more significantaffinity with respect to iron than with respect to copper and stabilizethe α phase of iron more than the γ phase of iron.
 13. A double-layeredsintered contact member produced by sinter bonding the copper basedsintered contact material of any one of claims 1 to 3 to an iron basedmaterial, containing Si, Al, Ti and Cr which expand a sintered layerand/or one kind of non-metallic particles which restrains a shrinkage ofa sintered layer, for fear that when using the double-layered sinteredcontact member which has been produced through a process in which amixed powder having a sintered contact material composition andcontaining Sn and/or Pb is dispersed onto a steel plate, subjected tofirst sinter bonding at 810° C. or more, and then subjected to secondsintering by mechanically increasing the density of the sintereddispersed powder layer, the layer of the mixed powder dispersed in thefirst sintering might peel off the steel plate owing to sintershrinkage.
 14. A double-layered sintered contact member produced bysinter bonding the copper based sintered contact material of any one ofclaims 1 to 3 to an iron based material, containing Si, Al, Ti and Crwhich expand a sintered layer and/or one kind of non-metallic particleswhich restrains a shrinkage of a sintered layer, for fear that whenusing the double-layered sintered contact member which has been producedthrough a process in which a mixed powder having a sintered contactmaterial composition and containing Sn and/or Pb is dispersed onto asteel plate, subjected to first sinter bonding at 810°0 C. or more, andthen subjected to second sintering by mechanically increasing thedensity of the sintered dispersed powder layer, the layer of the mixedpowder dispersed in the first sintering might peel off the steel plateowing to sinter shrinkage, wherein Sn is added by utilizing a Cu—Snbased alloy powder containing Sn in an amount no less than Cu—30 wt % Snand/or Sn primary powder, so that the sintered layer in the firstsintering is expanded.
 15. The copper based sintered contact materialaccording to any one of claims 1 to 3, further containing 12 to 16 wt %Sn and a Cu—Sn compound phase which is dispersedly precipitated in thestructure thereof, further containing one or more alloy elementsselected from the group consisting of Zn, Mn, Be, Mg, Ag, and Bi, and asolid lubricant such as MoS₂, CaF₂ and WS₂.